A new family of USB-to-serial bridge devices offers a straightforward way to interface with RS-232 or RS-485 serial networks through USB, using a minimum of components and printed-circuit-board space. The XR21B1420, XRB21B1422, and XRB21B1424 from Exar feature 1, 2, and 4 UART channels respectively. Also, the XRB21B1421, replete with single-channel UART, uses the native operating system HID (Human Interface Device) driver.
The XR21B142x devices fully comply with the USB 2.0 (Full-Speed) specification, maintaining a 12-Mbit/s USB data-transfer rate and delivering high data throughput, especially when multiple channels are operating simultaneously. Large 512-byte transmit (TX) and receive (RX) FIFOs enable maximum data throughput of 9 Mbits/s across up to four UART channels.
The family incorporates ±15-kV electrostatic-discharge (ESD) protection on the USB pins, eliminating the need for additional protection components and saving space. The devices also feature an internal oscillator, removing the need for an external crystal. The devices can be powered directly from the USB host’s 5-V supply. Furthermore, an integrated low-dropout linear regulator provides a regulated 3.3-V output.